Frequency changing device



FREQUENCY CHANGING DEVICE Filed Dec. 11, 1939 auRRE/v r 1 Geo/9 E PgfimINVENTOR.

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' A complete frequency atented Apr. 7, 1942 FREQUENCY CHANGING DEVICEGeorge H. Polnn, Olmsted Falls, Ohio, assignor of one-half to E. M.Heavens and one-half to Closman P. Stocker Application December 1 1,1939, Serial No. 308,671

Claims.

This invention relates to static frequency changers and moreparticularly to frequency changers which depend upon the saturation of amagnetic core for operation. a

In the past frequency changers have been made for converting onefrequency to another by means of saturable magnetic cores used intunedcircuits. However, it has been necessary to utilize output filtersfor obtaining the desired frequency whenever an approximate sine waveoutput was desired. Also, frequency changers of the past have reliedupon a construction which made it advisable to supply the changedfrequency from a non-linear or saturable impedance.

By means of my invention I depart from the prior art by supplying thechanged frequency from a linear impedance which is a part of thefrequency changing circuit rather than from a filter circuit which isfed by the saturable element. I have developed a static type frequencychanging system which is much simpler than the frequency changercircuits known in the prior art. By the use of my invention 1 am able toobtain wave forms on the output of the frequency changer whichapproximate a sine wave.

changer capable of producing this result can be made according to myinvention by arranging in a novel circuit relation three simpleelements, that is, a saturable inductance, a linear inductance and acapacitor. It is well to observe that the frequency is changed directlywithout the use of auxiliary exciting circuits and that the changedfrequency having a good wave form is obtained without the use offilters. Furthermore, I am enabled to obtain even or odd harmonics ofthe input frequency from such an arrangement without the use. of directcurrent excitation, the use of double core construction on the saturableelement, or the use of a magnetic bias on the iron core. In either casethe wave form of the output frequency is good.

It is an object of my invention to change the frequency of analternating current to either an even multiple or an odd multiple of thesupply frequency.

It is another object of my invention to produce even harmonics of analternating current supply by using in a novel circuit relation acapacitor, a non-linear inductance and a linear inductance, without anexternal bias being applied to the core of the non-linear inductance.

It is another object of my invention to produce even harmonics of analternating current supply by using in a novel circuit a capacitor, 9.nonlinear inductance and a linear inductance and by utilizing 'aself-exciting phase shifting mechanism to generate a new frequency.

It is another object of my invention to provide a frequency changer inwhich the output fre-' quency is supplied from a linear inductance inthe circuit.

It is another object of my invention to provide a frequency changer inwhich a capacitor is used as a tuning element common to two tunedcircuits each of different frequency.

It is an object of my invention'to provide a complete static typefrequency changer having only three necessary circuit elements arrangedin a novel circuit relation. j

It is an object of my invention to provide a parallel ferro-resonantcircuit in a frequency changer to generate a new frequency and to assistin separating the applied frequency from the new frequency.

It is another object of my invention to cause substantially the wholevoltage of the applied frequency to appear across a substantiallyantiresonant circuit included in a frequency changer.

It is another object of my invention to provide a frequency changercircuit having a capacitor as a commontuning element for at least twocircuits tuned to different frequencies and in which the two tunedcircuits are operated as parallel combinations with respect to theirrespective exciting means.

lit is another object of my invention to substantially eliminate thevoltage of'the supplied frequency in the output of a static frequencychanger without the use of output filters.

It is a further object of my invention to utilize a self-exciting phaseshifting mechanism to generate a new frequency.

It is another object of my invention to make use of a phase displacementof the voltage between two elements in'a frequency changer to separatethe supply frequency from the output frequency.

It is another object of my invention to balance out and separate voltageof the supply frequency from the voltage of the output frequency in afrequency changer by connecting an output impedance at approximatelynull points or equipotential points with respect to voltage of thesupply frequency but which points are not at equipotential with respectto voltage of the output frequency.

It is a further object of my invention to cause, in a frequency changer,a large current of the changed frequency and a small current of thesupplied frequency to flow through the impedance supplying the voltageto be utilized.

It is still a further object of my invention to provide a new method orarrangement of separating the changed frequency from the supplyfrequency in a static type frequency changer circuit.

Other objects and a fuller understanding of my invention may be had byreferring to the following description and claims taken in conjunctionwith the accompanying drawing in which like parts are designated by likereference characters and in which:

Figure 1 shows one embodiment of my fretion on the saturable inductiveelement. Other quency changer which is capable of supplying either evenor odd harmonics of the input frequency depending upon the adjustment ofthe various circuit elements.

Figure 1A shows an assumed circuit approximately equivalent to thecircuit shown in Figure l; the non-linear element of Figure 1 isrepresented in Figure LA by a linear element and a harmonic generator.

Figure 2 shows a modification of the frequency changer as shown inFigure 1 in which the saturable element has been changed to use asmaller value of capacitance.

Figure 3 is a modification of Figure 2 in which the condenser connectionhas been changed to give an alternative method or arrangement ofbalancing out the supply frequency from the output.

Figure 3A shows voltage-current characteristics of Figure 3, and

Figure 3B shows the input voltage-current characteristics which manifesta change in predominant frequency with variation in input voltage.

with reference to Figures 1, 1A, 2, 3, 3A and 3B in which correspondingparts are indicated by the same reference characters, it will be seenthat my frequency changer utilizes in a novel circuit a capacitor, anon-linear inductance and a linear inductance.

It is well known in the prior art that new frequencies may be obtainedfrom circuits using the three elements mentioned above, but a frequencychanger made in accordance with my invention operates in a fundamentallydifferent manner and produces a changed frequency of flood wave formwithout the use of additional parts or auxiliar circuits.

'Iypical frequency changers of the static type shown in the prior artmay be found in such circuits as shown and described in U. '8. PatentsNos. 1,587,512, 1,698,284, 1,782,348, 1,877,703, or 2,150,386; or in somof the more recent publications such as the article entitled MagneticGeneration of a- Group of Harmonics" by E. Peter: son J. M. Manley andL. R. Wrathall, pages 995- 1001, in Electrical Engineering, August 1937.

In reviewing the prior art it will be evident that in general thefrequency changer circuits contain many parts which are intended to actas filters 'or which in some other way are used to reduce the distortionof the output wave obtained from the frequency changer. Also it will benoted that in general. the output frequency or changed frequency issupplied to a load which is taken directly from the non-linear inductiveelement. In order to produce even harmonics of the supply frequency bycircuits of the prior art, it was necessary to apply an external bias tothe non-linear inductance. This was done circuits use rectifiers in thefilter circuit as a means of obtaining even harmonics of the appliedfrequency.

By my invention as shown in Figures 1, 2 and 3, I am able to get even orodd harmonics having excellent wave form by the use of only threereactive circuit elements.

With reference to Figure 1, the frequency changer circuit compriseswinding II on saturable core it connected in parallel relation withcapacitor 12 and this combination is connected in series with winding I4on a substantially linear core l3. Core II has an additional winding IIfor supplying power of the changed frequency to a load. Source ofalternating current i0 supplies powerto this combination and dependingupon the tuning of the various circuit elements, it is possible toobtain even or odd the input frequency from output winding ll. As willbe recognized non-linear inductance II is the element which generatesthe new frequencies in co-operation with the other circuit elements. Inthe circuit shown in Figure 1, an approximately anti-resonant conditiont the applied frequency is obtained by tuning non-linear inductance IIwith capacitor I2. Capacitor I! also cooperates with linear inductanceIt to form a tuned circuit for the new frequency. I prefer to have theimpedance of inductance l4 linear over the operating range. My circuitcontains only three essential elements and may have one or two differenttuned circuits. Where two tuned circuits ar used the capacitor isutilized to tune blothirircuits with an inductive element in each c rcuI shown as ap proximately equivalent to non-linear inductance H,although many details have been omitted for purposes of simplifyingtheexplanation.

the re r values of circuit constants are selected it 1; p

sible to have capacitor I! act as a common tunlinear inductance ll, totune the circuit comprising generator ll, inductance I4 and capacitor I!to be substantially anti-resonant to the changed or new frequency.

In the frequenc changer ure 1, non-linear inductance II and capacitor I!are tuned to approximately an anti-resonant condition with respect tothe frequency of source In and the circuit operates to supply thechanged frequency from output winding l5. As previously ointed out inconnection with Figure 1A, the impedanc of winding I4 is adjusted withcapaciwr I: to form an approximately anti-resonant circuit to the outputfrequency. By referringto Figure 1A, it will be observed that theanti-rescnant circuit to the new frequency is connected in parallelcircuit relation with respect to generator ll of th new frequency. Byoperating the circuit comprising inductive impedance I4 and capacitiveimpedance I! in the neighborhood of anti-resonance I obtain a distinctadvantage when supplying energy of the new frequency to a unity powerfactor load because with th circuit connection as shown a load connectedto output winding I5 is effectively connected across the anti-resonantcircuit and variations in load resistanc do not tend todetunc thecircuit. Therefore, variations in load resistance between zero andinfinitive do not appreciably affect the generation of the newfrequency.

By way of example it might be assumed that 180 cycles per second isdesired from output winding l5 and that source H) has a frequency of 60cycles per second. Capacitor l2 and nonlinear inductance are then tunedto approximately an anti-resonant condition with respect to the 60cycles and inductance I4 is tuned with capacitor l2 to approximately ananti-resonant condition with respect to the 180 cycles. Inductance II isproportioned to saturate within the range of voltage supplied by sourceIII while the impedance of inductance H remains substantially linear. Insuch a circuit, saturation of the nonlinear inductance ll generatesharmonics of the input frequency and a current flows in the 180 cycletuned circuit. Tests show that by maintaining an anti-resonant circuitto the 180 cycles a small current of the harmonic frequency flowsthrough saturable inductance ll while a large current of the harmonicfrequency flows in the anti-resonant circuit consisting of condenser l2and linear inductance element H. Therefore, in operation theanti-resonant circuit comprising non-linear inductance H and capacitorl2 limits the 60 cycle current flowing through linear inductance H to avery low value and the voltage induced in inductive element M will be,for practical purposes, only the harmonic voltage. With the circuitoperating as explained the predomi nant harmonic current through linearinductance M will be of the desired frequency and energy of thisfrequency may be supplied to a load connected to output winding l5.

With the circuit as shown in Figure 1 in operating condition,measurements indicate that practically the whole of the 60 cycle voltageof source I!) appears across capacitor [2 and nonlinear inductance H andthat very little appears across the inductance element l4.

Observations made by means of an oscillograph element in series withinductance l4 and source In show that substantially all of the currentflowing through inductance I4 is 180 cycle current. Because capacitor I2is common to both circuit shown in Fig- I anew tuned circuits it hasboth 60 cycle and 180 cycle circuit shown in Figure 1 there is someresidual voltage impressed across it. Non-linear inductance I I beingconnected in parallel with capacitor I! also has voltages of bothfrequencies impressed across it, controlling its saturation and thegeneration of the new frequency. From this observation, I find that thenew frequency is automatically separated from the supply frequency bythe novel construction and operation of a frequency changer made inaccordance with my invention, and filters are unnecessary for practicalpurposes.

Although I have explained the operation of the circuit shown in Figure lby assuming capacitor l2 and inductance l4 tuned to 180 cycles, I havebeen able to change the tuning of these two elements to obtain cycleswhich is an even har monic of 60 cycles or 300 cycles which is the fifthharmonic of {50 cycles. Any of these new frequencies may be obtainedwith wave forms which are good approximations of the sine wave whenvtaken directly from output winding l5. In my invention, the resistanceof the circuit elements is preferably low. I

It is possible to obtain even harmonics from the without the use ofexternal bias or any equipment other than that shown in the diagram. Inview of the fact that it is generally considered necessary to bias themagnetizable core to produce even harmonic distortion in a non-linearinductance such as element II, a question is presented as to the exactmethod of operation when the even harmonics are generated. One possibleexplanation is that magnetism in core l6 of inductive element H, tesimaleven harmonic distortion. This even harmonic distortion causes in thefirst instance a feeble 120 cycle current to flow through capacitor l2,inductive element and saturable inductive element H. phase to increasefurther the even harmonic distortion in inductive element ll therebycausing an even increasing 120 cycle current to flow until a normaloperating value is reached. The action is cumulative and the 120 cyclecurrent through the tuning elements l2 and It quickly builds up to alarge value.

When 120 cycles is obtained from a circuit as shown in Figure 1,- thewave form is good and approximates a sine wave. Furthermore, undercertain circuit conditions it is possible to gradually load outputcircuit l5 and supply 120 cycles to the load until an approximatelyshort circuit load condition exists. The generated frequency disappearsonly when the output winding i5 is short circuited and then just as soonas the short circuited condition is removed the generated frequencyalmost instantaneously reappears and builds up to its original strength.

Although the. above explanation of the operation of my frequency changerseems to be substantiated by observations and measurements, I do notwish to be bound or to limit the scope of my invention by thisexplanation.

The frequency changing circuit shown in Figure 2 uses the non-linearinductance 20 as a stepup transformer which permits the use of a smallercapacity of higher voltage rating compared with the capacitor used inthe circuit shown in Figure 1. However, the frequency changer in Figure2 operates the same as explained in connection with Figure 1.

It can be shown that with this type of con struction the sameanti-resonant circuits are present in Figure 2 as are shown in thesimplified which introduces infini- This current is in the proper andassumed diagram of Figure 1A. Laboratory data tends to indicate thatthere is one difference between the circuits of Figures 1 and 2. Thisdifference resides in the fact the internal impedance ofthe generator ofthe new frequency is not the-gsame for Figure 2 as for the circuit shownin Figure 1. This change in internal impedance does not seem to make anydifference in the operation, except where output winding I5 is connecteddirectly into another similar static type frequency changer in cascade.In this case if the first frequency changer is constructed as shown inFigure 2, the output of the second frequency changer may be moredistorted than if the first frequency changer is constructed as shown inFigure 1. It is therefore evident that in some cases where space is afactor, some advantage is gained by the use of the circuit shown inFigure- 2, butin general where cascade operation of fre quency changersconstructed in accordance with my invention is contemplated, I havefound that the one shown in Figure 1 is preferably employed except forthe last stage.

In Figure 2 I have shown leads 38 and 39 which are connected acrosslinear inductance I4 for the purpose of supplying power of the newfrequencies to a load. Linear inductance Il may be used as an autotransformer to supply different voltages to a load by a tap such as 31on winding M. It is to be understood that the linear inductance H, asshown in Figures 1, 2, and 3, may be used as a choke, anauto-transformer or an insulating transformer.

Another modification of my frequency changer is shown in Figure 3 inwhich non-linear inductance is connected in series relation withcapacitor l2 and source of supply iii. In Figure 3 linear inductance His connected between intermediate tap 2| canon-linear inductance 20 andgenerator ID in such a way that a portion of the winding of non-linearinductance 20 and linear inductance H are connected in series relationwith generator l0. Although it is not necessary for intermediate tap 2|to be spaced exactly in the middle of the winding of non-linearinductance 20, I have found that very good results can be obtained whenintermediate tap 2| .is at the mid-point. I have, however, moved tap 2|to an off-center position and by changing the circuit constants,obtained good results. i

At first glance, Figure 3 seems to be entirely different from thefrequency changer circuit shownin Figure 2, but the only structuralchange is that capacitor I2 is connected to the opposite side of sourcel0. With the circuit connected as shown in Figure 3,- good operation maybe obtained with only one resonant circuit. In general, I prefer totune' the circuit comprising capacitor l2, inductive element I, togetherwith the leakage reactance of non-linear inductive 20 to the newfrequency; An operating difference exists between the -ircuit shown inFigure 3 and the circuits shown' in Figures 1 and 2. in that the voltageof the supply frequency isbalanced out of inductive element in Figure 3in a new and novel manner.

When non-linear inductive element 20 has a higher impedance to thefrequency of source l0 than capacitor |2, the voltage across non-linearelement 20 is substantially in phase with the voltage of source l0 andthe'voltage across capacitor I2 is approximately 180 out of phase withthe voltage of source l0. Under this condition there exists a point onthe winding of non-linear element 20, which is approximately at l2 wasapproximately half the valu through any other the same potential withres of source in as the side of nected to capacitor i2. Tap 2| ispreferably placed in or near this point on the winding of non-linearelement 20 which gives the minimum voltage of the frequency of source IDacross inductive element [4. Thus I make use of a phase displacement ofthe voltage between two elements in the frequency changer to separatethe supply frequency from the output frequency.

Although voltage of the supply frequency is balanced out of'outputimpedance H by connecting impedance H to points which are atapproximately equipotential with respect to the supply voltage, thevoltage of harmonics of the frequency of source In generated acrossnonlinear element 20 by the current flowing through it will appearacross element It. As in the previousv explanations, the circuit isarranged so that the generator of the new frequency works into anapproximately anti-resonant circuit so that there is no excessivecurrent drain on the generator of the new frequency to decrease itsvoltage. However, the circuit is tuned so that the current of the newfrequency flowing through non-linear element 20 aids in the generationof the voltage of the new frequency. The fact that current flow of thenew frequency through non-linear element 20 aidsin the generation ofvoltage of the new frequency across non-linear element 20 is evidencedby the fact that even harmonics of the frequency of source H) arereadily obtained in my frequency changer by proper tuning of inductiveelement H with the other circuit elements.

Test results indicated that with the circuit as shown in Figure 3,excellent operation can be obtained when tap 2| is at the mid-point ofthe winding of non-linear element 20. Tests made upon a device usingthis center tapped arrangement showed that the voltage of the frequencyof source It! across non-linear element 20 is approximately twice thevoltage of the frequency of source l0 acrosscapacitor l2. The current ofthe new frequency flowing through capacitor e of the current of the newfrequency flowing through linear element I. It can be seen that ifnon-linear element 20 is considered the generator of the new frequencyand linear inductive element It is connected across only half as manyturns as capacitor I2, then to maintain a condition of anti-resonancethe inductive current through linear element I4 would have to be twicethe capacitive current through capacitor i2. Experimental resultsindicate that the circuit is near a condition of anti-resonance withrespect to the new frequency. Under this condition inductance M willalwayshave a greater current of the new frequency through it than willflow single portion of the' circuit. I have observed the current flow invarious pect to the frequency the generator Ill conbranches of thefrequency changer as shown in 'source i0 and 180 c cycles flowed in allof the branches of the cirmately twice the found in anyoth Test resultsshowing the variations in current flow through linear inductance H withvariation of the voltage supplied by source ID, are shown in Figure 3A.Curve a shows the effective current through inductive element H which isa current of the same fundamental frequency as ource l0 together withharmonics of that frequency. Curve 1) shows the value of current flowingthrough inductance H which has the same fundamental frequency as sourcel0.

With reference to curve b it can be seen that the value of fundamentalcurrent, having the same frequency as source l0, passes through aminimum value betwen values of input voltage represented by c to d. Itwill be noted that the effective current represented by curve a isrelatively large compared with the current of the fundamental frequencywithin the input voltage range 0 to d. This means that inoperating afrequency changer tion the harmonic currents are greatly in excess ofthe fundamental currents. Because inductive element H has a much desiredfrequencies than to the fundamental frequency and also because the flowof the desired harmonic is much larger than the current of thefundamental frequency the output voltage delivered to a load will bepractically free of voltage of the frequency supplied by source In. Ihave found that the best operating range is between the limits 0 and dshown in Figure 3A.

Figure 3B shows the variation of the effective value of current suppliedto my frequency changer as the voltage of source Ill varies. A ratherunusual and unexpected feature of my invention ,is shown by the curve in313 which is that as the input voltage is gradually increased theeffective current assumes and different output'frequency predominates.It is togbe understood that this result is obtained without readjustingany of the circuit elements. In one of the devices tested the suppliedfrequency was 60 cycles. The predominate frequencyof the outputfrequency changer between the limit m and n and 0 and p was 180 and .300cycles respectively. From this result it can be seen that my frequencychanger can be used quencies without altering any of its elements.

Throughout the description and in the following claims I refer to linearinductance. By this I mean a substantially linear inductance element. Asuitable linear inductance may be made with an iron core having an airgap in series with the magnetic path and may comprise a choke coil, atransformer with insulated windings, or an auto transformer. The term"non-linear inductance means a saturable inductance or an inductancewhich changes its impedance for various values of current flowingthrough it. Also I mention resonant and connection with inductanceswhich are either substantially linear or non-linear. It 'is-t'o beunderstood that such circuits need not be sharply tuned to the desiredfrequencies because the inductive elements contain iron or othermagnetic material and the impedance may currents through the inductiveelements. ever, in the case of cults involving the non-linear inductanceelements these may be understood to be either in series ferro-resonanceor parallel ferro-resonance as the case may be.

Although I have described my invention with a Howin accordance with myinvenhigher impedance to the the shape 'of a series a of plateaus and aseach plateau is reached a new voltage delivered by my vary with the reonant or anti-resonant cirby way of example, and that to produce twodistinct frequency,

anti-resonant circuits in I it is understood been made only numerouschanges in the details of construction on the combinations andarrangement of parts may be resorted to without departing from thespirit and scope of the invention as hereinafter claimed.

I claim asmy invention:

1. A frequency changing circuit for obtaining a new frequency from analternating current source comprising, in combination, a linearinductance, a capacitor and a non-linear inductance having anintermediate tap forming a first winding means and a second windingmeans, said linear inductance and said first winding means beingconnected in series with the alternating current source, said capacitorand said second winding means being connected in series with each otherand shunting the linear inductance, and output means connected to thelinear inductance.

2. A frequency changing circuit for obtaining a new frequency from analternating current source comprising, in combination, ductance, acapacitor and a non-linear inductance, said linear inductance and saidnon-linear inductance establishing a series circuit with the alternatingcurrent source, said non-linear inductance generating a new frequencydifferent from the frequency of the supply source, said capacitor beingconnected to the alternating current source in circuit relation with thesaid linear and non-linear inductance and establishing two substantiallyanti-resonant circuits, the capacitive effect of the capacitor and thereactive effect of the non-linear inductance building up an antiresonantcondition with respect to the frequency of the alternating currentsource and the capacitive effect of the capacitor and the reactiveeffect of the ,linear inductance building up an antires'onant conditionwith respect to the new frequency, and output means connected to thelinear inductance for giving the new frequency, said capacitor and one'of said inductances being connected in closed circuit with the supplysource and the other said inductance being in a closed electricalcircuit including the capacitor.

3. A .Z'equency changing circuit adapted to be connected to a source ofalternating current and generate new frequency comprising, incombination, a linear inductance, a capacitor, and a non-linearinductance, said capacitor and nonlinear inductance being connected toform a parallel combination and generating the new freand means forconnecting said parallel combination in circuit with ,said linearinductance and the source of alternating current, said capacitor andsaid linear inductance forming a closed circuit with the supply sourceand having substantially equal and opposite impedance values withrespect to the new frequency to cause substantially all of the voltageof the new frequency to appear across the linear inductance.

4. A frequency changing circuit adapted to be connected to a source ofalternating current and certain degree of particularity, that thepresent disclosure has generate a new frequency comprising, incombination, a linear inductance, a capacitor, and a non-linearinductance, said capacitor and nonlinear inductance being connected incircuit relation to form a parallel combination and generating the newfrequency,

said parallel combination being connected in series with said linearinduct! ance and the source of alternating current and delivering to thelinear inductance the new generated frequency, said capacitor and saidlinear inductance forming a closed circuit with the supa linear in- Iply source and having substantially equal and op posite impedance valueswith respect to the new frequency to cause substantially all of thevoltage of the new frequency to appear across the linear inductance, andoutput means for obtaining the new frequency from said linearinductance.

5. A frequency changing circuit adapted to be connected to a source ofalternating current and generate a new frequency comprising, incombination, a linear inductances non-linear inductive element and acapacitor forming two substantially anti-resonant circuits to separatethe new frequency from the frequency of the source of alternatingcurrent, said non-linear inductive element and said capacitor beingconnected in circuit relation to form a parallel combination andgenerating the new frequency, said parallel combination comprising oneof said anti-resonant circuits and being anti-resonant to the frequencyof the source of alternating current, said parallel combination beingconnected in series with the linear inductance and the source ofalternating current and delivering to the linear inductance the newfrequency, said capacitor and said linear inductance forming a closedcircuit with the supply source and being anti-resonant to the newfrequency and comprising the other anti-resonant circuit, said capacitorconstituting a tuning element common in both anti-resonant circuits, andoutput means for supplying the new frequency from the linear inductance.

6. A frequency changing circuit adapted to operate from an alternatingcurrent source utilizing three reactive elements to form two antiresonant circuits for generating a new frequency and separating the newfrequency from the fre-- quency of the alternating current source com,-prising, in combination, a linear inductance, a non-linear inductance,and a capacitor, said nonlinear inductance and capacitor forming a firstcircuit anti-resonant to the frequency of the altemating current sourceand generating a new frequency, said linear inductance and capacitorforminga second circuit anti-resonant to the new frequency, said firstcircuit and the linear inductance being connected in circuit relationwith each other and the alternating current source to causesubstantially all the voltage of the new frequency to appear across thelinear inductance, and output means to supply the new frequency from thelinear inductance, said ca pacitor and one of said inductances beingconnected in closed circuit with the supply source and the other saidinductance being in a closed electrical circuit including the capacitor.

7. A frequency changing circuit adapted to be connected to a source ofalternating current i and generate a new frequency comprising, in

combination, a linear inductance, a capacitor, and a non-linearinductance having an inter mediate tap, said non-linear inductance andsaid capacitor being connected in series with each other and with thesource of alternating current and generating the new frequency, saidlinear inductance being connected to the intermediate tap on thenon-linear inductance to a point common to the capacitor and the sourceof alternating current, said non-linear inductance and said capacitordelivering to the linear inductance the new frequency,.and output meansfor supplying the new frequency from the linear inductance.

8. A frequency changing circuit adapted to be connected to a source ofalternating current and generate a new frequency comprising, incombination, a linear inductance, a capacitor, and a non-linearinductance having an intermediate tap, said non-linear inductance andsaid capacitor being connected in series with each other and with thesource of alternating current and generating the new frequency, saidlinear inductance being connected to the intermediate tap on thenon-linear inductance to a point common to the capacitor and the sourceof a1- ternating current, said non-linear inductance and said capacitordelivering to the linear inductance the new frequency, and output meansfor supplying the new frequency from the linear inductance, saidintermediate tap on the nonlinear inductance being electrically selectedto cause substantially all the voltage of the new frequency to appearacross the linear inductance.

9. A frequency changing circuit adapted to 0perate from an alternatingcurrent source utilizing three reactive elements to form twoantiresonant circuits for generating a new frequency and separating thenew frequency from the frequency of the alternating current sourcecomprising, in combination, a linear inductance, a non-linearinductance, and a capacitor, said nonlinear inductance and capacitorbeing connected in parallel and generating the new frequency and forminga first circuit anti-resonant to the frequency of the alternatingcurrent source, said linear inductance and capacitor forming a secondcircuit anti-resonant to the new frequency. said first circuit andlinear inductance being connected in circuit relation with each otherand the alternating current source to cause substantially all thevoltage of the new frequency to appear across the linear inductance, andoutput means to supply the new frequency from the linear inductance.

10. In combination with an alternating current source, a linearinductance and an antiresonant circuit connected in circuit relationwith each other and with the alternating current source to form afrequency changing circuit, said anti-resonant circuit beingsubstantially anti-resonant to the frequency of the alternating currentsource nd comprising a non-linear inductance and a capacitor and causingharmonics of the frequency of the alternating current source to appearacross said linear inductance, said capacitor and one of saidinductances being connected in closed circuit with the supply source andthe other said inductance being in a closed electrical .circuitincluding the capacitor.

GEORGE H. POHM.

